a diffrent kettle of fish
a new problem that makes your old problem look easy
You thought your math test was hard. Now you’ve got a math test and your dog ate your notes.
You had a small debt. Now you’ve got a small debt, a big debt, and a debt you don’t even know about.
You had a small problem. Now you’ve got a small problem, a big problem, and a problem that involves your mom’s ex.